Epidemiologic evidence is accumulating that early-life factors may play an important role in the etiology of breast cancer. Children and adolescents may be particularly sensitive to exposures that are associated with breast cancer initiation or protection against breast cancer, thus presenting new windows of opportunity to potentially modify breast cancer risk at a young age. Identification of modifiable early-life risk factors is particularly important for girls from breast cancer families as they are at increased risk of developing breast cancer, given their family history. We are planning to establish a multi-center cohort of 1,600 girls aged 6-17 years and follow them prospectively in order to study early-life exposures (perinatal, lifestyle, and environmental exposures), as well as genetic and epigenetic factors and their effects on several endpoints related to pubertal development, including age at menarche, breast development, breast tissue characteristics, and sex and growth hormones. The cohort, named LEGACY (Lessons in Epidemiology and Genetics of Adult Cancer from Youth), will consist of girls and their mothers who are enrolled in the Breast Cancer Family Registry (BCFR) and, for comparison, girls and their mothers identified through friend controls. Thus, the cohort will be enriched with girls at increased breast cancer risk, given their family history. In preparation for establishing such a cohort, we propose to pilot test the baseline and 6-months follow-up procedures in order to 1) demonstrate feasibility of recruitment and retention in the cohort, and 2) obtain preliminary data on prevalence and variability of key endpoint and exposure variables. We will build upon a small pilot study and recruit an additional 50 girls and their mothers (30 BCFR girls and 20 friend control girls) from the San Francisco Bay area. The baseline assessment includes an interview and self-administered questionnaire, anthropometric measurements, collection of biospecimen samples, and a 7-day pedometry study. Data and biospecimen collection will be repeated 6 months after the baseline assessment. Experience gained from this pilot study will be essential for the planning and establishment of the full cohort. PUBLIC HEALTH RELEVANCE: We propose to conduct a pilot study with 50 girls aged 6-17 years and their mothers in order to demonstrate the feasibility of recruitment and retention. Experience gained from this pilot study will help establish a cohort of 1,600 girls that will be followed for 5 years in order to study early-life exposures and their effects on pubertal development.